German Patent Application No. 35 40 8 11 describes a fuel injection system for controlling a solenoid-valve-controlled fuel pump for a diesel internal-combustion engine. The system comprises a pump piston which moves in a pump chamber and is driven by the camshaft. The pump piston pressurizes the fuel in the pump chamber. The fuel is then pumped to the cylinder of the internal-combustion engine via a fuel line.
A solenoid valve is positioned between a fuel supply tank and the pump chamber. An electronic control unit delivers control pulses to the solenoid valve. The solenoid valve opens and closes in response to these control pulses. In response to the position of the solenoid valve, the pump piston pumps fuel into the combustion chamber of the internal-combustion engine.
The trigger times of the control pulses determine the start and end of fuel injection, and also, therefore, the fuel quantity to be injected. After a pulse gear on the crankshaft generates a synchronous pulse, a counter is started which counts the pulses on an incremental gear located on the camshaft. As a function of the prevailing motor speed and other parameters, the control element controls the start and end of the injection process. To optimally operate the internal-combustion engine under variable operating conditions, it is necessary to determine the start of injection and the injection quantity as precisely as possible as a function of engine-specific data and existing operating conditions. Because the motor speed is not constant, actual conditions, and in particular, delay times and rotational irregularities of the engine, must be considered when determining the trigger times for the solenoid valve.
In order to obtain the desired accuracy in calculating the trigger times, the angular velocity of the camshaft must be known. The angle covered during a constant time, and thus also the quantity of fuel injected, depend upon the instantaneous angular velocity. An irregular angular velocity, as well as the torsional and driving rigidity of the camshaft, may result in calculation errors. At a constant cam (lift) speed, the injected fuel quantity is proportional to the angle which the camshaft covers during the trigger time, and is independent of the start of injection. In reality, however, the instantaneous rotational speed of the camshaft, and thus also the cam speed, are not constant. This leads to errors in determining the injected fuel quantity.
These errors depend upon the changes in cam speed and rotational speed, which are not considered in the calculation, or on compressional waves and manufacturing tolerances. Known injection systems can consider these influences only conditionally, because they are based on the form of a non-automatic control, and not on the form of an automatic control.